LLNL Researchers Melt Diamond Using Omega Laser

How Scientists Melted Diamond Using the Omega Laser

Melting diamond requires extreme conditions that conventional ovens cannot provide. The LLNL research team utilized the OMEGA laser at the University of Rochester’s Laboratory for Laser Energetics. The facility houses a 10.8-foot target chamber where 60 ultraviolet beams—frequency-tripled from infrared to 351 nanometers—deliver up to 30 kilojoules of energy onto a target in pulses ranging from 100 picoseconds to 4 nanoseconds.

When the laser beams flash-vaporize the target’s surface, the material blasting outward generates a powerful shock wave that compresses and heats the underlying diamond in a single hit. To capture atomic changes within a one-nanosecond window, researchers deployed a separate set of X-ray beams timed to scatter off the sample while the shock wave moved through it. Optical instruments recorded the temperature and shock speed simultaneously. Millot noted that watching shock-compressed diamond with X-ray diffraction all the way to melting point was a first, made difficult because carbon is a light atom that scatters very few X-rays.

Why Solid Diamond Floats on Its Own Liquid

The experiments revealed an unexpected physical behavior: solid diamond floats on its own liquid. As pressure climbed toward 145 million psi, the melting temperature dropped slightly. According to LLNL scientists, squeezing a material to make it melt more easily indicates that the liquid packs tighter than its own solid—the same property that allows ice to float on water.

Jon Eggert, an LLNL scientist whose earlier experiments 20 years ago first pointed toward this floating behavior, watched the diffraction data confirm the phenomenon. The new data also corrected LLNL’s previous temperature readings by more than 1,000 degrees. Theory suggested carbon might switch into a denser crystal structure called BC8 at high pressures—a phase hinted at in earlier shots on Sandia National Laboratories’ Z machine. However, Millot’s team found no trace of BC8, concluding that a single shock leaves atoms too little time to rearrange, trapping the crystal in the diamond structure until it liquefies.

Implications for Planetary Interiors and Fusion Energy

These findings provide concrete data for planetary scientists modeling ice-giant planets like Neptune and Uranus. Current models suggest carbon crystallizes deep inside these planets and rains down toward the core as diamond. Because the laser experiments reached pressures beyond those found in ice-giant interiors, researchers now possess verified benchmarks rather than mathematical extrapolations.

The findings also impact inertial confinement fusion research at the National Ignition Facility (NIF), where fuel capsules are encased in a diamond shell. The initial shock of an implosion must melt this shell into a smooth fluid to prevent solid lumps from creating flaws that cause the reaction to fail. LLNL’s simulations indicate that a gentler first shock would melt the shell just as completely, leaving the internal fuel more compressible and potentially tripling energy gains, provided other implosion degradations remain controlled.

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